docs: def get_section_key_line(self, data, key, opt_extension=''):
          """Get the next section line for a given key.
  
          :param data: the data to proceed
          :param key: the key
          :param opt_extension: an optional extension to delimit the opt value
  
          """
          start = 0
          init = 0
          while start != -1:
              start = self.get_next_section_start_line(data[init:])
              init += start
              if start != -1:
                  if data[init].strip().lower() == self.opt[key] + opt_extension:
                      break
                  init += 1
          if start != -1:
              start = init
          return start